Internal combustion engines may include water injection systems that inject water from a storage tank into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions. As mentioned above, water may be stored in a vehicle to provide water for injection on demand. However, in order to meet the water injection demands of an engine, a vehicle needs to have a sufficient supply of water. In one example, a water storage tank of a water injection may be manually refilled by a vehicle operator. However, in some situations, water for refilling the tank may not be readily available and having to re-fill the tank may be undesirable for the operator.
Other approaches to refilling a water storage tank includes collecting water (or condensate) from other vehicle systems on-board the vehicle, such as collecting water from an air conditioning (AC) system. For example, the approach shown by Kohavi and Peretz in US 20110048039 includes extracting water from an air conditioning system. Therein, collecting condensate is based on an amount of water stored in a water storage reservoir (e.g. tank). However, the inventors have recognized potential issues with such methods. In particular, collecting water opportunistically from an AC system when the AC system is already operating may be insufficient to meet the water injection demands of an engine. Additionally, if an AC compressor of the AC system is operated using energy stored at a battery (e.g. an electric AC system), as may be the case in a hybrid electric vehicle, the battery may not have enough stored electrical energy to operate the AC system when water is needed. Further, if excess electrical energy is available, the AC compressor may be operated to maximize water collection under conditions with a reduced fuel economy penalty.
In one example, the issues described above may be addressed by a method for a hybrid vehicle including adjusting an AC compressor loading of an electric AC system and a ratio of friction to regenerative brake torque during braking based on a level of water in a water reservoir coupled to a water injection system. A water injection system, including the water reservoir, may be fluidically coupled to the electric AC system. Thus, when the AC compressor is run (e.g., as the AC compressor load increase), water may be collected from the electric AC system and stored at the water reservoir for use in the water injection system. During a braking event, a portion of the electrical power generated during the braking event may be used to operate the AC compressor based on the water level in a water reservoir. In this way, the AC compressor may be operated during a braking event to collect water for a water injection system, thereby providing water for injection via the water injection system. For example, adjusting the AC compressor load and the ratio of friction to regenerative braking may include decreasing the ratio of friction to regenerative braking and running the AC compressor from energy generated from the regenerative braking system to increase the AC compressor load in response to the water level in the water reservoir (e.g. tank) being less than a threshold level. When a battery of the hybrid vehicle is not able to store charge, all energy recovered from regenerative braking may be directed to run the AC compressor. However, when water collection for the water injection system is needed and the battery is able to store energy, energy recovered from regenerative braking may be directed to both the AC compressor and battery, thereby providing energy for the AC compressor and battery in response to demand. In this way, energy recovered from the regenerative braking system may be used to run the AC compressor and collect water for the water injection system. As a result, the water reservoir of the water injection system may be replenished automatically without manual filling and without draining the battery of the hybrid vehicle. Further, the AC compressor may be run and water for injection collected, even when the battery cannot accept charge from the regenerative braking system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.